Ca2+-induced Ca2+ release (CICR) enhances a variety of cellular Ca2+ signaling and functions. How CICR affects impulse-evoked transmitter release is unknown. At frog motor nerve terminals, repetitive Ca2+ entries slowly prime and subsequently activate the mechanism of CICR via ryanodine receptors and asynchronous exocytosis of transmitters. Further Ca2+ entry inactivates the CICR mechanism and the absence of Ca2+ entry for >1 min results in its slow depriming. We now report here that the activation of this unique CICR markedly enhances impulse-evoked exocytosis of transmitter. The conditioning nerve stimulation (10–20 Hz, 2–10 min) that primes the CICR mechanism produced the marked enhancement of the amplitude and quantal content of end-plate potentials (EPPs) that decayed double exponentially with time constants of 1.85 and 10 min. The enhancement was blocked by inhibitors of ryanodine receptors and was accompanied by a slight prolongation of the peak times of EPP and the end-plate currents estimated from deconvolution of EPP. The conditioning nerve stimulation also enhanced single impulse- and tetanus-induced rises in intracellular Ca2+ in the terminals with little change in time course. There was no change in the rate of growth of the amplitudes of EPPs in a short train after the conditioning stimulation. On the other hand, the augmentation and potentiation of EPP were enhanced, and then decreased in parallel with changes in intraterminal Ca2+ during repetition of tetani. The results suggest that ryanodine receptors exist close to voltage-gated Ca2+ channels in the presynaptic terminals and amplify the impulse-evoked exocytosis and its plasticity via CICR after Ca2+-dependent priming.
Many scientists have devoted themselves to the study of the interaction between subwavelength structures and electromagnetic waves. These structures are commonly composed of regular arrays of subwavelength protuberances, which can be artificially designed. However, extending from 2D periodic patterns to 3D disordered subwavelength structures has not been studied yet. In this study, we studied the total diffuse reflectivity of carbon aerogels with various 3D networks of randomly oriented particle-like nanostructures by using normally incident visible light (430-675 nm). We observed that the different 3D network nanostructures of carbon aerogels, especially for the structures with the minimum size, reduced the reflectivity effectively. It was found that the key mechanism for the subwavelength-structure-induced ultralow reflectivity property is due to the decrease of the amplitude of electron vibration forced by the electromagnetic wave, which provides a simple method for designing perfect black materials.
Nonsteroidal anti-inflammatory drugs, such as ketoprofen, are generally used to treat pain and inflammation and as pyretic agents in clinical medicine. However, the usage of these drugs may lead to oxidative injury to the gastrointestinal mucosa. Camellia oil ( Camellia oleifera Abel.) is commonly used in Taiwan and China as cooking oil. Traditional remedies containing this oil exert beneficial health effects on the bowel, stomach, liver, and lungs. However, the effects of camellia oil on ketoprofen-induced oxidative gastrointestinal mucosal lesions remain unknown. The objective of this study was to evaluate the effect of camellia oil on ketoprofen-induced acute gastrointestinal ulcers. The results showed that treatment of Int-407 cells with camellia oil (50-75 μg/mL) not only increased the levels of heme oxygenase-1 (HO-1), glutathione peroxidase (GPx), and superoxide dismutase (SOD) mRNA expression but also increased vascular endothelial growth factor (VEGF) and prostaglandin E2 (PGE2) protein secretion, which served as a mucosal barrier against gastrointestinal oxidative injury. Moreover, Sprague-Dawley (SD) rats treated with camellia oil (2 mL/kg/day) prior to the administration of ketoprofen (50 mg/kg/day) successfully inhibited COX-2 protein expression, inhibited the production of interleukin-6 (IL-6) and nitrite oxide (NO), reversed the impairment of the antioxidant system, and decreased oxidative damage in the gastrointestinal mucosa. More importantly, pretreatment of SD rats with camellia oil strongly inhibited gastrointestinal mucosal injury induced by ketoprofen, which was proved by the histopathological staining of gastrointestinal tissues. Our data suggest that camellia oil exerts potent antiulcer effects against oxidative damage in the stomach and intestine induced by ketoprofen.
1. The effects of the phosphodiesterase inhibitors caffeine, theophylline, isobutylmethylxanthine (IBMX) and rolipram on spontaneous electrical activity (slow waves) were studied in the circular muscle of the guinea‐pig gastric antrum. 2. All the inhibitors reduced slow wave frequency without changing the membrane potential and the slow wave configuration, but at higher concentrations they blocked the slow waves and caused membrane hyperpolarization. In the presence of the inhibitors a low level of irregular electrical activity could be observed in many preparations. 3. Isoprenaline, forskolin, dibutyryl cAMP and 8‐bromo‐cAMP all produced effects essentially similar to those of phosphodiesterase inhibitors. K+ (12 mM) and removal of K+ both depolarized the membrane and these were not affected by IBMX (1‐3 microM). A decrease in frequency caused by IBMX was also not significantly affected by 12 mM K+ or K+ removal and only partially antagonized by TEA or 4‐aminopyridine. 4. These results suggest that an increase in intracellular cAMP inhibits pacemaker activity of slow waves. An increase in K+ conductance does not seem to be a major factor in this inhibition. Slow waves appear to be a compound electrical activity in a group of muscle cells and are likely to be disintegrated by xanthine derivatives.
The subject of topological materials has attracted immense attention in condensed-matter physics because they host new quantum states of matter containing Dirac, Majorana, or Weyl fermions. Although Majorana fermions can only exist on the surface of topological superconductors, Dirac and Weyl fermions can be realized in both 2D and 3D materials. The latter are semimetals with Dirac/Weyl cones either not tilted (type I) or tilted (type II). Although both Dirac and Weyl fermions have massless nature with the nontrivial Berry phase, the formation of Weyl fermions in 3D semimetals require either time-reversal or inversion symmetry breaking to lift degeneracy at Dirac points. Here we demonstrate experimentally that canted antiferromagnetic BaMnSb 2 is a 3D Weyl semimetal with a 2D electronic structure. The Shubnikov-de Hass oscillations of the magnetoresistance give nearly zero effective mass with high mobility and the nontrivial Berry phase. The ordered magnetic arrangement (ferromagnetic ordering in the ab plane and antiferromagnetic ordering along the c axis below 286 K) breaks the time-reversal symmetry, thus offering us an ideal platform to study magnetic Weyl fermions in a centrosymmetric material.topological material | nontrivial Berry phase | 3D semimetal T he observation of the quantum Hall effect has led to the discovery of new phases associated with topological ordering. In the past decade, topological materials have emerged as a new frontier of condensed matter physics due to new physical concepts and potential applications. Theory has played a major role in predicting new topological materials, which have been realized experimentally. Topological insulators, which are metallic at the surface but insulating in bulk (for a review, see ref. 1), have been extensively investigated. Surface states in these materials can be described by the Dirac equation with the Fermi surface formed by Dirac points. Dirac fermions are effectively massless because their dispersion is linear in energy. If the bulk is superconducting, the surface hosts Majorana fermions (for a review, see ref.2). More recently, a new class of topological materials, namely, Dirac or Weyl semimetals, has appeared. Such topological semimetals are characterized by the presence of electron and hole pockets touching with either degeneracy (Dirac) or nondegeneracy (Weyl). If both time reversal and inversion symmetries are preserved, the system is a Dirac semimetal (3). If either time-reversal or inversion symmetry is broken, the Dirac points split and turn into Weyl points, making the system a Weyl semimetal (3). If both timereversal and inversion symmetries are broken, the system may become a Weyl superconductor (4).The above framework makes the search of topological semimetals possible. For example, Dirac semimetals should have centrosymmetry to preserve the inversion symmetry. However, a noncentrosymmetric crystal structure would favor Weyl semimetal configuration (5). If a system is centrosymmetric and magnetically ordered, whether time-reversal sy...
In circular muscle preparations isolated from the guinea pig gastric antrum, regular spontaneous electrical activity (slow waves) was recorded. Under normal conditions (6 mM K+), the frequency and shape of the slow waves were similar to those observed in ordinary stomach smooth muscle preparations. When the resting membrane potential was hyperpolarized and depolarized by changing the extracellular K+ concentration (2–18 mM), the frequency of slow waves decreased and increased, respectively. Application of cromakalim hyperpolarized the cell membrane and reduced the frequency of slow waves in a dose-dependent manner. Cromakalim (3 μM) hyperpolarized the membrane, and slow waves ceased in most preparations. In the presence of cromakalim, subsequent increases in the extracellular K+ concentration restored the frequency of slow waves accompanied by depolarization. Also, glibenclamide completely antagonized this effect of cromakalim. In smooth muscle strips containing both circular and longitudinal muscle layers, such changes in the slow wave frequency were not observed. It was concluded that the maneuver of isolating circular smooth muscle altered the voltage dependence of the slow wave frequency.
Lycopene and its metabolite apo-10'-lycopenoic acid have been shown to induce phase II detoxifying/antioxidant enzymes through activation of the nuclear factor erythroid-derived 2-like 2 (Nrf2)-antioxidant response element (ARE) transcription system. However, little is known about whether apo-8'-lyocpenal, one of the main metabolites of lycopene in rat livers, in lycopene-containing food, and in human plasma, has similar effects. This study investigated the effect of apo-8'-lycopenal on Nrf2-ARE system-mediated heme oxygenase 1 (HO-1) and NAD(P)H:quinine oxidoreductase 1 (NQO-1) expression in human HepG2 cells. It was found that apo-8'-lycopenal (1-10 μM) significantly increased nuclear Nrf2 accumulation, ARE-luciferase activity, Nrf2-ARE binding activity, chymotrypsin-like activity, and downstream HO-1 and NQO-1 expression, but decreased cytosolic Kelch-like ECH-associated protein 1 (Keap1) expression. Results also revealed that the ERK/p38-Nrf2 pathway is involved in activation of HO-1 and NQO-1 expression by apo-8'-lycopenal using Nrf2 siRNA and ERK/p38 specific inhibitors. In addition, the activation time of lycopene on nuclear Nrf2 accumulation is slower than that of apo-8'-lycopenal, suggesting that the chemopreventive effects of lycopene may be partially attributed to its metabolites.
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